For 8 I’d reccomend starting with either Storm Warning from the main range (more of a classic series feel), or Doom Coalition from the boxsets (more of a modern series feel). The 11th Doctor Chronicles are also extremely good (volume 3 and onward, including Broken Hearts, is the Valerie stuff you may have heard about). The War Doctor stuff with Jonathan Carley is also very good, if you’re into that
For spin offs, I love the War Master range, and Dark Gallifrey is mostly pretty good
It’s probably worth asking here how long the car ride is, and how much you care about story arcs, going in order, and skipping stories